Catenanes—molecules comprising two interlocking rings held together like links in a chain—are topologically non-trivial: a catenane is a topological isomer of its separated rings, but the rings cannot be disconnected without bond scission. Catenanes can exist as topological enantiomers if both rings have directionality conferred by a defined atom sequence, but this has led to the assumption that the stereochemistry of chiral catenanes composed of oriented rings is inherently topological in nature. Here we show that this assumption is incorrect by synthesizing an example that contains the same fundamental stereogenic unit but whose stereochemistry is Euclidean. One ring in this chiral catenane is oriented by the geometry of an exocyclic double rather than determined by atom sequence within the ring. Isomerization of the exocyclic double bond results in racemization of the catenane, confirming that the stereochemistry is not topological in nature. Thus, we can unite the stereochemistry of catenanes with that of their topologically trivial cousins, the rotaxanes, enabling a more unified approach to their discussion.

链烷——由两个互锁环组成的分子，就像链条中的链环一样——在拓扑学上是非常重要的：链烷是其分离环的拓扑异构体，但如果没有键断裂，环就不能断开。如果两个环都具有由定义的原子序列赋予的方向性，则链烷可以作为拓扑对映体存在，但这导致了这样的假设，即由定向环组成的手性链烷的立体化学本质上是拓扑的。在这里，我们通过合成一个包含相同基本立体单位但其立体化学为欧几里得的示例来证明该假设是不正确的。这种手性链烷中的一个环是由环外双环的几何结构定向的，而不是由环内的原子序列决定的。外环双键的异构化导致链烷的外消旋化，证实立体化学本质上不是拓​​扑的。因此，我们可以将链烷的立体化学与其拓扑上微不足道的表亲轮烷的立体化学结合起来，从而为他们的讨论提供更统一的方法。